1. Field of the Invention
The present invention relates to an image formation apparatus such as a copying machine and, more particularly, to an apparatus which has an image density control function for determining an optimal image formation condition for each image formation.
2. Description of the Prior Art
A conventional copying machine is known which has an automatic density control function (to be referred to as AE hereinafter) for measuring the original density and for controlling image formation conditions such as the charge amount, the light exposure amount or quantity, or the developing bias voltage in accordance with the detection result of the original density.
In a copying machine of this type, AE measurement is performed prior to or simultaneously as the copy sequence. Therefore, even if the AE measurement result does not indicate optimal image formation conditions, the copy may be produced, resulting in a miscopy.
Furthermore, AE measurement does not provide satisfactory results for all types of originals. In other words, satisfactory AE measurements cannot be performed for some type of original (e.g., an original having an area to be subjected to AE measurement, which has a density extremely different from the rest of the original).
Another copying machine is known wherein the surface potential of a photosensitive drum is measured and the potential control light quantity control is performed on the basis of the measured surface potential. A copying machine of this type frequency uses a microcomputer for performing control of the overall sequence. Special display units or indicators are required to display the control contents.
With recent development in LSI techniques, a multi-functional and high-precision microcomputer has been realized. An A/D converter which has conventionally required a special separate IC can now be integrated into a 1-chip microcomputer. With this technique, analog data (information) is frequently supplied directly to a microcomputer and is processed in a software manner.
For this reason, data processing is a "black box" and cannot be monitored externally.
Meanwhile, a microcomputer incorporated into a copying machine controls displays and indicators at the control section of the machine, and the copying density control which has been conventionally performed by lever operation is now processed digitally.